Deep-hardening boron steels



- Patented Apr. 21, 1942 OFFICE DEEP-HARDENING BORON STEELS WalterCrafts, Niagara Falls, N. Y., assignor to Electro Metallurgical Company,a. corporation of West Virginia No Drawing.

Application January 5, 1940, Serial N0. 312,491

Claims. (Cl. 759123) This invention relates to steels, and morespecifically to steels the hardness of which may be increased by rapidcooling from temperatures within or above the critical range. For thesake of simplicity of presentation, the application of the inventionwillbe described herein principally as it may be applied to carbon steelscontaining 0.1% to 1% carbon, up to about 2% manganese,

and up to about 1% 81110011; but as the description proceeds it will beevident that the invenable steels.

When hardening steels by rapid cooling from taken into solid solution insteel at high temperatures, for instance boron, silicon, molybdenum,

, tungsten, chromium, or nickel. These hardening tion may be applied toa wide variety of hardenhigh temperatures, it is often-desired toproduce a deep or thick zone of'hardened material rather than a thin orshallow hardened case. The depth to which a piece of steel will harden,at a given rate of heat extraction, is different in difierent steels.The property of the steel which involves this relative susceptibility tomass effect in hardening seems to be inherent, and for convenience itwill be termed herein deep-hardenability.

An accepted, convenient measure of deephardenability is afforded by theJominy" test, described in detail in A Hardenability Test forCarburizing Steel by W. E. Jominy and A. L.

Boegehold, Trans. Am. Soc. for Metals, vol. 26,

p. 574 (1938). To summarize briefly, the test is made on a small bar ofsteel of standardized shape and dimensions. and comprises heating theentire bar to the desired hardening temperature, quickly extracting heatthrough one end face of the bar, grinding off superficial scale anddecarburized skin and producing a flat surface suit able for making a,hardness test, and measuring the Rockwell C hardnessalong the length ofthe bar. As a means for readily expressing the relation between thehardness and distance from the hardened end, the distance from thehard-' ened end at which the hardness becomes less than Rockwell C" 50is used and is referred to herein as the Jominy depth. If the 'samehardening temperature and cooling conditions be used for a series ofsteels, the relative depths of the hardened zones indicate the relativedeephardenability of the steels of that series, each to the others.

An object of this invention is to improve the deep-hardenability ofhardenable steels generally, and of plain carbon and low alloy (lessthan 5% inthe aggregate of elements other than iron and carbon) steelsespecially.

The deep-hardenability of steel may be en hanced in some degree by.adding in suitable percentages any one of the elements which can beabove-listed elements may be used to impart an even further enhanceddeep-hardenability without substantial sacrifice of other. desirableproperties of the steel. I have further observed that combinationsof'certain ofthese elements with suitable percentages of one or'more ofthe alkali metals; alkaline earth metals, beryllium, aluminum, titanium,zirconium, uranium, cerium, thorium, vanadium, columbium, and tantalum,considerably enhance the effect of the combination ondeep-hardenability.

In the course of my research on this subject I have discovered, that afew of these combinations of elements are particularly effective inimparting deep-hardenability, and the present invention is based on thisdiscovery.

A particularly eiiective combination is boron and silicon, preferablywith one or more of the further elements aluminum, beryllium, magnesium,calcium, barium, strontium, the alkali metals, titanium, zirconium,cerium, hafnium, thorium, vanadium, columbium, tantalum, uranium, in asuitable proportion greater than that required for grain refinement.

In accordance with the present invention, boron may be present in apercentage between 0.0005% and 0.05%, but should tween about 0.001% and0.015%. The silicon contentmay suitably be between 0.1% and 1% or 2%,and will usually be between 0.15% and 0.35%. The minimum totalproportion of said further element or elements to be'added is anyproportion greater than that required for grain refinement, andpreferably up to several times that required for grain refinement. Thepercentage required for grain refinement will depend on the kind ofsteel, the steel-making conditions, and the kind and number ofdeoxidizing and grain-refining elements used, and may be determinedempirically by the methods now in common use by metallurgists' andsteelmakers. In most instances the total percentage of such furtherelements to be added will be between 0.03% and 0.5% or 1%, and apreferred range is between 0.05% and 0.3%.

ordinarily .be beawunmswnmmmwmaamsmmn manmmmewamaunumnme J'ominy we ma du N kUmw m m gt... eaeeceostmwwmmm Qnw0 nw m opmppmmm mmmmmmmmmmm I an ea a a a e e no 0 Q00 000000000 Q0 I TableC 0 mg... m o o o o tungsten,molybdenum,

mmmmmm emwmm Table D mm msmesemg Percentage 01 elements added Percentageoi elements added Percent Percent Percent Percent Percent PercentPercent Percent Percent Percent depth Table D is similar to Tables :eand 0, except that the relative eflfects of various combinations ,0!three, four, and live elements of the group aluminum. calcium,zirconium, vanadium, and

titanium are indicated.

For each element and each combination oi elements there appea s to be anoptimum perlIardenabilit depth Percent Percent The relatively greatemcacy of combinations of 7 boron and silicon maybe appreciated irom an15 Each of the steels in Table A containsa total proportion of theelements aluminum, zirconium, 5 and .vanadiumslightlv above thatrequired for centage .which imparts a maximum depth of hardenability anda frequent result oi an increase in percentage beyond the optimum is ade- 5 I crease of deep-hardenability below that imparted by the optimum.For reasons of economy, or to; obtain a steel having a certain desiredco'mbina tion of physical properties, it will'often beds sired to addeither lessor more of the elements than will impart a maximum depth orhardening. Hence, the invention is notlimited to the use of the optimumpercentages.

inspection of the figures, derived from test data. in Table Awhichindicat'e the relative Jominy hardenability depths, in hundredthsof an inch, of steels containing about 0.45% carbon, 1.5% manganese, theindicated added percentage oi other elements, and the remainder iron.

Percent Percent Percent mess remmmm mswmmmw 0 0 0 & 0 0 G0 0"0 &0 0 0 0grain refinement. It will be observed that neither 0.25% silicon nor0.01% boron alone has any substantial effect on the deep-hardenabilityof the fine-grained steel; but that the addition of both silicon andboronincreasesthe deep-hardenability to a remarkable extent. 1

The respective and relative eflects. of additions of the single elementsaluminum, zirconium, vanadium, and titanium on the deep-hardenability45. of steels containing about 1.6% Mm-0.25% Si, 0.45% to 0.55% carbon,and 0.01%-added boron, are indicated by the figures in Table 18, derivedfrom test data. The carbon contents of the None.

' The fact that considerable deep-hardenability is impartedbv-any of alarge number o1'combi-' nations 0! elements is an important one, becausethe latitude in'choice or elements aflords an through selections!appropriate combinations. f In general, the deep-hardening steel of bestqual- .o.oo 0.025 0.05 0.10 0.15 00 ityior mostpurposes-wlll be obtainedby the ad ments" described above,zwit hin the range 0! per-' suggestedherein; 'Ifhis generalization holds true not only for the steels oi the8. All. 85 ,iaifi type (medium manganese oil hardening) g j chosen forpurposesot exempliflcation in Tables 4 -B C, and D, but for low-alloysteels oiiall types,

including those containing one or more ot'the opportunity to control thecleanness, rain size, tensile streng h, and toughness oi. the steeldition of more 'two'ot the "further clenot to beunderstood that allproperties neces- -sarily improve in a consistent procession as thenumber and percentage of added elements .in-

elements chromium, nickel, phosphorus, sulfur, etc.- However, it isTable C is similar to Table B, except that it indicates the relativeeffect of the addition of varicreases. .It must be borne in mind thatthe rel- J5 ative effectiveness 01 different elements is not the Irected) Iominy hardness depth (coraluminum, calcium, zirconium,vanadium, and

steels used in such tests rangedtrom 0.42% to 50 I Elementadded.

Alumlnmn .--.e--.. Titanium.. Zlrconium- Vanadium......;.

\ '"Not determined.

and the percentages of are the percentages added to the steel justbefore Rockwell 50.

by test data of the physical properties oi several representative steelsafter forging,

from 850 C., and drawing at 400, C. for one hour. In Table E, theindicated percentages 01" carbon and manganese are by analysis, thepercentage of silicon in all steels is 0.25%, nominal, the remainingelements casting. In Table F, the yield point (Y. P.) and tensilestrength (T. S.) of the steels of Table E are given in thousands ofpounds per square inch; a two inch initial gage length, and per cent R.A. designates percentage reduction in area, upon fracture of the 0.505inch diameter standam (A. S. T. M.) tensile test specimens. Under Izodare given the Izod impact test results, in foot-pounds, using. astandard specimen onecentimeter square with standard V notch one mm.deep. The Jominy Hardness Depth is that actually measured, in hundredthsof an inch, to

Table E Composition of steels (rest substantially iron and 0.25% Si)Steel Per- Per- Per- Per- Per- Per- Per- Per- Percent cent cent centcent cent cent cent cent C Mn B A] Ca V Zr Ti Cr 1 L 0A 51 7 (101 0.501.7 0.01 0.15 g) 0.50 1.6 0.01 0.07 0.07 0.51 1. 6 0.01 0.07 0.07 0.491.7 0.01 0.07 0.07 g) 0.49 1.6 0. 01 0.07 0.07 v() 0.46 1. 6 0.01 0.070. 07 0.50 1.6 0.01- 0.035 0.035 0.49 1. 7 0.01 0.025 0.025 0.0250.49 1. 7 0.01 0.035 0.035 0.035 0.49 1. 7 0.01 0.035 0.035 0.035 0.0350.51 1.6 0. 01 0.035 0.035 0. 035 .0. 035 0.50 1. 7 0. 01 0.025 0.0250.025 0.025 0.025 0.48 .74 0.035 5') 0.035 0.035 1.0 0.50 .75 0.01 0.0350.035 0.035 1.0

:None

Table F Properties of steels of Table E Steel N0. t P t I d J ercenercen zo ominy 8 El 11. A. depth -In all of the Jominy hardness testsused as the bases of figures used in the tables herein, the samehardening temperature and cooling conditions were used.

As described in applications filed jointly by Walter Crafts and James H.Critchett, Serial El. designates percentage elongation in.

quenching I 3 Numbers 201,931 (Patent 2,221,781) 7 and 201,932

(Patent No. 2,221,782), both filed April 14, 1938;

and Serial Numbers.243,324(Patent No. 2,221,783) and 243,325 (Patent No.2,269,407) both filed Debarium, strontium, boron, aluminum; (2)titanium, zirconium, cerium, hafnium, thorium; (3)

yanadium, columbium, tantalum, elements from at least two groups beingpresenteach in an amount preferably at least3%; or (B) at least 3% ofeach of at least two elements selected from the group titanium,zirconium, cerium, hafnium, and thorium. In general, it is preferredthat the sumof the elements other than iron and silicon be between 10%and.20%, and not exceed at the most 25% plus an additional percentagewhich equals 5% multiplied by the number oi. elements in excess of two.For grain refinement, it is not ordinarily necessary to add more of thecomplex deoxidizing agent than enough to increase the silicon content ofthe steel by 0.25%. Thus, the maximum percentage that is reallynecessary for these purposes will not ordinarily exceed 1% of the ironor steel.

. The complex deoxidizing agents described'in the saidprior applicationsare admirably suited for use in accordance with the present invention,provided they. are used in a proportion greater than that required forgrain refinement.

Such hardening agents as for instance boron I may be introduced into thesteel with the deoxidizing andgrain refining agent, for instance as aningredient of, one of the above-described complex deoxidizing agents, orit may be separately introduced into the molten steel either before,during, or after the addition of the deoxidizing and grain refiningagent. Boron, for example, may be added to molten steel as borax,calcium borate, boron carbide or ferro-boron, i. e. in almost anyconvenient form.

The advantages of the invention may be expointed in any of several ways.For instance, the cheaper steels among those described above may be usedinstead of more expensive, more highly alloyed steels heretofore used toobtain the desired strength. Or, present high strength steels may beeven further strengthened by applying the principles of the invention,either by deeper hardening to a lower average hardness or by deeperhardening to the same or even higher hardness. Among the various steelsdescribed, there is a wide range of choice in respect to such factors ascost, grain size control, ductility, strength, toughness, and types ofinclusions. Thus, the invention is capable of a wide field ofapplication, which will be apparent to metallurgists and steelmakers.Therefore, although numerous specific examples have been given herein toillustrate the principles of the invention, it will be understood thatsuch examples are merely illustrative and do not restrict the inventionbeyond the requiremen of the claims and the state of the art.

I claim:

1. Method of imparting increased deep-hardenability to a hardenablesteel which comprises adding to such steel while it is molten betweenand between 0.03% and 1%.

grain refining element in a total percentage greater than that requiredfor grain refinement 2. 'In the method'deflned in claim 1, provementwhich comprises maintaining the boron content or the steel between0.001% and 0.015%,- the siliconcontent between 0.15% and 1%, and theamount or grain-refiningelement added is between 0.03% and 1%.

. .3. Method of imparting improved deep-hardenability to a hardenablesteel which comprises adding boron and silicon thereto and adjusting theproportions of such elements in said steel to at least 0.0005% butmaterially less than 0.05% boron and between about 0.50% and 2% silicon.

4. Method as "defined in claim 3, wherein the proportion of boron isbetween 0.001% and 0.015%and the proportion of silicon is between about0.50% and 1.00%.

5'. In' a hardenable steel,'at least 0.0005% but materially less than0.05% boron and about 0.50% to 2% silicon which boron and silicon impartimproved deep-hardenability to said steel,

7 remainder iron and incidental impurities.

6. In a hardenable steel, 0.0005% to 0.015% boron; 0.1% to 1% silicon;and at least one further element chosen from each of the groupsconsisting of (1) aluminum, magnesium, calcium,

, barium, strontium, the alkali metals, and (2) titanium, zirconium,:cerium, hafnium, thorium,

the im- 0.1% and of silicon, at least 0.001% but mate'- .boron; betweenrially less than 0.05% boron, and at least one,

i v 0.1% and 2%- silicon; at least one further element of the groupconsist- 1115.0: aluminum, magnesium, calcium, barium, strontium, and'the alkali metals. in a total percentage greater than that required forgrain reilnement and between about 0.03% and 1%.

8. Method of imparting improved deep-hardenability toahardenable steelwhich comprises adding thereto between 0.0005%' and 0.05%-

boron; between 0.1% and 2% silicon; and at least one further elementotjthe group consisting of titanium, cerium, hafnium, thorium, vanadium,columbium, tantalum,- and uranium, in a total percentage greater thanthat required for grain refinement and between about 0.03%,and

9. Method of imparting improved deep-hardenability to a hardenablesteel-which comprises addin thereto between 0.0005%' and 0.05%

boron; between 0.1% and 2% silicon; and at least one further elementirom each of the groups consisting respectively of (1) aluminum,magflnesium, calcium? barium, strontium, and the vanadium, columbium,tantalum, and uranium,

. in a total percentage'greater than that required for grain refinementand between 0.03% and 1%, which boron, silicon, and further elementsimpart improved deep-'harden'ability to said steel;

alkali. metals, and (2) titanium, cerium, hafnium,

thorium, vanadium, columbium, tantalum, d uranium; the total percentageof such further elements being greater than that required for grainrefinement and being between about 0.03% and 1%.

10. Method of treating molten steeloi a hardenable type to improve itsdwp-hardenability when solidified, which comprises adding thereto0.0005% to 0.05% boron'and an amount, greater than that required forgrain refinement but less 0.01% to 1% carbon; manganese in a substantialproportion not over 2%; remainder iron.

'7. Method of imparting improved deep-hardeenability to ahardenablesteel which comprises adding 'thereto between 0.0005% and0.015%

than 5%, of a composition of matter containing iron, 25% to silicon, andat least two iur= 'ther elements selected from the group titanium,

zirconium, cerium, hafnium, thorium, vanadium, columbium, tantalum, anduranium, the total amount of said further elements being between about3% and about 20%.

